In this competing renewal of HD 29550, we build on our previous studies of the dynamics of nonmarital fertility by: (1) modeling the behavioral subprocesses underlying a premarital first birth;(2) distinguishing between the union contexts in which pregnancies yielding a first birth occur and are resolved;(3) developing and estimating formal behavioral models in which discounts of future alternatives may vary with age;and (4) initiating studies of male nonmarital fertility. To model the subprocesses underlying a premarital first birth, we examine how the onset of sexual activity, occurrence of romantic relationships, and accumulation of human capital influence women's premarital first birth risks in the period following sexual onset. To examine the multiple union contexts in which pregnancies leading to a first birth occur and are resolved, we model the non-random selectivity of conceptions to single, cohabiting, and married women and ask if other unobserved factors help account for an observed change in union status between conception and birth. To examine the consequences of a nonmarital conception, we describe trends in the stability of shotgun marriages. To investigate apparent inconsistencies in the perceived costs of childbearing versus contraception, we develop and estimate formal behavioral models to clarify the potential roles of myopia, time inconsistency, uncertainty, and misperception bias.} To examine men's nonmarital fertility, we investigate the quality of male fertility and union histories and, conditional on data quality, undertake studies of male nonmarital fertility that will complement our knowledge of female nonmarital fertility. We propose a multidisciplinary research team incorporating new insights, methods, and models to the study of these questions. We analyze data from the 1980, 1985, 1990, and 1995 June Current Population Surveys, the 1979 and 1997 Longitudinal Surveys of Youth, the 1995 and 2002 National Surveys of Family Growth, and the 1998-2000 Fragile Families. When possible, we compare findings across multiple data sources. We focus throughout on births that occur prior to a first marriage, recognizing that such births occur within heterogeneous union and social contexts, and to men and women possessing both observed and unobserved characteristics.